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Lexical Elements of the DEC Text Processing Utility Language
4.8 Expressions
A true value in DECTPU is any odd integer; a false value is any even integer. Use
the logical operators (AND, NOT, OR, XOR) to combine one or more expressions.
DECTPU evaluates Boolean expressions enclosed in parentheses before other
elements. The following example shows the use of parentheses to ensure that the
Boolean expression is evaluated correctly:
IF (X = 12) AND (y <> 40)
THEN
.
.
.
ENDIF;
4.9 Reserved Words
Reserved words are words that are defined by DECTPU and that have a special
meaning for the compiler.
DECTPU reserved words can be divided into the following categories:
• Keywords
• Built-in procedure names
• Predefined constants
• Declarations and statements
The following sections describe the categories of reserved words.
4.9.1 Keywords
Keywords are a DECTPU data type. They are reserved words that have special
meaning to the compiler. You can redefine DECTPU keywords only in local
declarations (local constants, local variables, and parameters in a parameter list).
If you give a local constant, local variable, or parameter the same name as that of
a keyword, the compiler issues a message notifying you that the local declaration
or parameter temporarily supersedes the keyword. In such a circumstance, the
keyword is said to be occluded. See Chapter 3 and the DEC Text Processing
Utility Reference Manual for more information on keywords.
4.9.2 Built-In Procedure Names
The DECTPU language has many built-in procedures that perform functions such
as screen management, key definition, text manipulation, and program execution.
You can redefine DECTPU built-in procedures only in local declarations (local
constants, local variables, and parameters in a parameter list). If you give a
local constant, local variable, or parameter the same name as that of a built-in
procedure, the compiler issues a message notifying you that the local declaration
or parameter temporarily supersedes the built-in. In such a circumstance, the
built-in is said to be occluded. See the DEC Text Processing Utility Reference
Manual for a complete description of the DECTPU built-in procedures.
4.9.3 Predefined Constants
The following is a list of predefined global constants that DECTPU sets up. You
cannot redefine these constants.
• FALSE
• TPU$K_ALT_MODIFIED
• TPU$K_CTRL_MODIFIED
4–12 Lexical Elements of the DEC Text Processing Utility Language